Microwave filter loss mechanisms and effects

The losses in coupled cavity filters due to coupling apertures, tuning screws, and surface roughness have been determined experimentally. The results show, for example, that the shapes of the coupling apertures have a significant effect on filter losses. They may be used to estimate how the effective unloaded Q of a filter, and thus its insertion loss, varies as a function of bandwidth, configuration (e.g., single- or dual-mode), and response type (e.g., Chebyshev or elliptic). Also, they may be used to predict other effect such as response skewing and spatial distribution of dissipated power.